Off the top of my head (I am in a generative AI field but I haven't done text lately): You can use an LLM (best to use the model underlying ChatGPT, DaVinci-00

Off the top of my head (I am in a generative AI field but I haven't done text lately): You can use an LLM (best to use the model underlying ChatGPT, DaVinci-003, itself) and see how unlikely is the next predicted token. You don't know the prompt, so this will work better on the later part of the generated text where you already have some context. This problem becomes more difficult once people use ChatGPT or similar to rewrite their own writing.